Method for fabricating capacitor of semiconductor device

ABSTRACT

A method for fabricating a capacitor of a semiconductor device on a semiconductor substrate can includes an insulating film formed on the substrate. A plug is formed in the insulating film, the plug electrically connected with the semiconductor substrate. A lower electrode is formed on the plug and the insulating film adjacent to the plug. A Ta 2 O 5  film is formed on the lower electrode and the insulating film adjacent to the lower electrode. The Ta 2 O 5  film is oxidized by flowing oxygen under the ambient of hydrogen gas at a temperature of between about 800° C. and 850°C. An upper electrode is formed on the Ta 2 O 5  film on the lower electrode and the insulating film adjacent to the lower electrode.

RELATED BACK

[0001] The present application claims priority to Korean PatentApplication No. P2000-69658 filed on Nov. 22, 2000, the disclosure ofwhich is hereby incorporated into the present application by reference.

FIELD OF INVENTION

[0002] The present invention relates to a semiconductor device, and moreparticularly, to a method for fabricating a capacitor of a semiconductordevice that prevents a lower electrode from being oxidized, therebyimproving a leakage current characteristic of the device.

BACKGROUND OF THE INVENTION

[0003] It is known to densely pack DRAM modules on a semiconductordevice to achieve a desired capacitance. However, the size of the DRAMand the area of the capacitor must be reduced to achieve the desireddensity. A Ta₂O₅ film that can obtain high capacitance in a relativelysmall area can be used as a dielectric film for such a capacitor.

[0004] When the Ta₂O₅ film is used as the dielectric film, silicon canbe used as a lower electrode of the capacitor. However, a dopingconcentration of the silicon can adversely lower the capacitance of thecapacitor.

[0005] A capacitor having a metal-insulator-metal (MIM) structure can beused to avoid this disadvantage. In the MIM structure, a lower electrodeis formed of a metal. In particular, it is known to form the lowerelectrode from tungsten (w).

[0006]FIGS. 1A to 1E show cross-sectional views of a known method forfabricating a capacitor of a semiconductor device.

[0007] As shown in FIG. 1A, a first tetra ethyl ortho silicate (TEOS)film 12 and a first nitride film 13 are sequentially deposited on asemiconductor substrate 11. An oxidation process that uses O₂ isperformed.

[0008] Subsequently, the first nitride film 13 and the first TEOS film12 are selectively removed by photolithography and etching processes toform a contact 14 that exposes a portion of the semiconductor substrate1.

[0009] A second nitride film is deposited on a surface of thesemiconductor substrate 11 and then etched back such that the nitridefilm remains on a sidewall within the contact hole 14 to form nitridefilm spacers.

[0010] As shown in FIG. 1B, a polysilicon film is deposited on theentire surface of the semiconductor substrate 11 and into the contacthole 14. The polysilicon film is then etched back to form a plug 16 thatis disposed within the contact hole 14.

[0011] Subsequently, a second TEOS film 17 is deposited at apredetermined thickness and then selectively removed by thephotolithography and etching processes, thereby forming a trench 18 thatexposes the plug 16 and a surface of the first nitride film 13 adjacentto the plug 16.

[0012] As shown in FIG. 1C, a tungsten film 19 is formed by a sputteringmethod and a chemical vapor deposition (CVD) method. A surface of thetungsten film 19 formed by the CVD method is very rough.

[0013] A third TEOS film 20 and a spin on glass (SOG) film 21 aresequentially deposited into the trench 18. The SOG film 21 and the thirdTEOS film 20 are selectively removed by an etch-back process to expose asurface of the tungsten film 19 disposed outside of the trench 18.

[0014] As shown in FIG. 1D, the exposed tungsten film 19 is removed by aCMP process. The unexposed tungsten film 19 within the trench 18constitutes a lower electrode 19 a.

[0015] The remaining SOG film 21 and third TEOS film 20 are removed by awet etching process.

[0016] As shown in FIG. 1E, the second TEOS film 17 is removed by thephotolithography and etching processes.

[0017] A Ta₂O₅ film 22 is deposited on the surface of the semiconductorsubstrate 11. The Ta₂O₅ film 22 is then oxidized by a low temperatureultraviolet (UV)-ozone (O₃) process. The process uses light having awavelength of between about 250 to about 260 nm that is generated by anUV-lamp to irradiate O₃ produced by an O₃ generator. However, the lowerelectrode 19 a disposed below the Ta₂O₅ film 22 is also oxidized by thisprocess. The UV-O₃ process is performed at a low temperate to reduce thedegree of oxidation of the lower electrode 19 a

[0018] A titanium nitride (TiN) film or a tungsten(W) film is used asthe metal film for an upper electrode. The tungsten film is selectivelyremoved by the photolithography and etching processes such that the filmremains on the Ta₂O₅ film 22 disposed on the lower electrode 19 a andremains on a region adjacent to the lower electrode 19 a to form anupper electrode 23. Thus, a capacitor of a known semiconductor device isfabricated.

[0019]FIG. 2 shows the surface of the lower electrode formed oftungsten. The upper portion of the lower electrode 19 a was formed bythe CVD method. The lower electrode 19 a and the Ta₂O₅ film wereoxidized during the UV-O₃ oxidation process. As shown in the figure, thesurface of the lower electrode 19 a is relatively very rough.

[0020] The high surface roughness of the lower electrode 19 a results ina relatively high application of an electric field at discreet portionsof the electrode. The conventional method for fabricating a capacitor ofa semiconductor device results in several disadvantages.

[0021] Since both the lower electrode as well as the Ta₂O₅ film areoxidized during the oxidation process of the Ta₂O₅ film, a leakagecurrent is increased due to a tunneling of electrons, as shown in FIG.3. Because the UV-O₃ process is performed at a low temperature to reduceoxidation of the lower electrode, an oxidation efficiency and thereforeelectrical characteristics of the Ta₂O₅ film are also decreased.

[0022] SUMMARY OF THE INVENTION

[0023] The invention provides a method for fabricating a capacitor of asemiconductor device on a semiconductor substrate that prevents a lowerelectrode from being oxidized, thereby improving a leakage currentcharacteristic of the device. An insulating film can be formed on thesemiconductor substrate. A plug can be formed in the insulating film,the plug electrically connected with the semiconductor substrate. Alower electrode can be formed on the plug and the insulating filmadjacent to the plug. A Ta₂O₅ film can be formed on the lower electrodeand the insulating film adjacent to the lower electrode. The Ta₂O₅ filmcan be oxidized by flowing oxygen under the ambient of hydrogen gas at atemperature of between about 800° C. and 850° C. An upper electrode canbe formed on the Ta₂O₅ film on the lower electrode and the insulatingfilm adjacent to the lower electrode.

[0024] Additional advantages and features of the invention will be setforth in part in the description which follows, and in part will becomeapparent to those having ordinary skill in the art upon examination ofthe following, and/or can be learned from practice of the invention. Theadvantages of the invention may be realized and attained as particularlypointed out in the appended claims.

[0025] To achieve these and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described, a methodfor fabricating a capacitor of a semiconductor device according to theinvention can include the steps of forming an insulating film on asemiconductor substrate; forming a plug electrically connected with thesemiconductor substrate through the insulating film; forming a lowerelectrode on the plug and the insulating film adjacent to the plug;forming a Ta₂O₅ film on a surface of the semiconductor substrate;oxidizing the Ta₂O₅ film by flowing oxygen under the ambient of hydrogengas of 800° C. to 850° C.; and forming an upper electrode on the Ta₂O₅film over the lower electrode and a region adjacent to the lowerelectrode.

[0026] It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory and are intended to provide further explanation of theinvention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings, which are incorporated herein andconstitute part of this specification, illustrate presently preferredembodiments of the invention, and, together with the general descriptiongiven above and the detailed description given below, serve to explainfeatures of the invention.

[0028]FIGS. 1A to 1E are sectional views of process steps showing aknown method for fabricating a capacitor of a semiconductor device.

[0029]FIG. 2 is a photograph taken of a surface of a lower electrodeformed of tungsten.

[0030]FIG. 3 is a graph showing leakage current depending on a biasvoltage of a capacitor of a known semiconductor device.

[0031]FIGS. 4A and 4B are cross-sectional views of process steps showinga method for fabricating a capacitor of a semiconductor device accordingto an embodiment of the invention.

[0032]FIGS. 5A to 5F are cross-sectional views of process steps showinga method for fabricating a capacitor of a semiconductor device accordingto another embodiment of the invention.

[0033]FIG. 6 is a graph showing leakage current depending on a biasvoltage of a capacitor of a semiconductor device according to theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0034] Reference will now be made in detail to the preferred embodimentsof the present invention, examples of which are illustrated in theaccompanying drawings.

[0035] A method for fabricating a capacitor of a semiconductor deviceaccording to an embodiment of the invention will be described withreference to FIGS. 4A and 4B.

[0036] A TEOS film 32 and a first nitride film 33 can be sequentiallydeposited on a semiconductor substrate 31. An oxidation process can beperformed under the ambient of O₂.

[0037] Subsequently, the first nitride film 33 and the first TEOS film32 can be selectively removed by photolithography and etching processesto form a contact hole that exposes a portion of the semiconductorsubstrate 31.

[0038] A second nitride film can be deposited on a surface of thesemiconductor substrate 31 and then etched back to form nitride filmspacer 34 on a sidewall within the contact hole.

[0039] A polysilicon film can be deposited on an entire surface of thesemiconductor substrate 31 and in the contact hole. The polysilicon filmcan be then etched back to form a plug 35 within the contact hole.

[0040] Subsequently, a tungsten film can be deposited on thesemiconductor substrate 31 by a sputtering method and a CVD method. Thetungsten film can be then selectively removed by The photolithographyand etching processes, such that the tungsten film remains on the plug35 and on the first nitride film 33 adjacent to the plug 35. By thismethod, a lower electrode 36 can be formed.

[0041] A Ta₂O₅ film 37 can be deposited on the surface of thesemiconductor substrate 31 and then oxidized.

[0042] Since tungsten can be actively oxidized by a small amount ofoxygen at a low temperature, the Ta₂O₅ film 37 can be oxidized under thefollowing process conditions to avoid oxidation of the lower electrode36 that is formed of tungsten.

[0043] The Ta₂O₅ film 37 can be oxidized by flowing oxygen under theambient of hydrogen gas at a temperature of between about 800° C. toabout 850°0 C. During the oxidation process, an amount of the hydrogencan be much more than an amount of the oxygen.

[0044] The Ta₂O₅ film 37 can be reoxidized by an UV-O₃ process. TheTa₂O₅ film 37 can be irradiated by light having a wavelength of betweenabout 250 to about 260 nm that can be generated by a UV-lamp, within anatmosphere of O₃ produced by an O₃ generator.

[0045] A metal film for an upper electrode can be deposited on the Ta₂O₅film 37. A titanium nitride (TiN) film or a tungsten(W) film can be usedas the metal film for an upper electrode.

[0046] The metal film for an upper electrode can be selectively removedby the photolithography and etching processes, such that the metal filmremains on the Ta₂O₅ film 37 on both the lower electrode 36 and a regionadjacent to the lower electrode 36. By this process, an upper electrode38 can be formed. Thus, a capacitor of a semiconductor device accordingto an embodiment of the invention can be fabricated.

[0047] As shown in FIG. 5A, a first TEOS film 42 and a first nitridefilm 43 can be sequentially deposited on a semiconductor substrate 41.An O₂-oxidation process can be performed under the ambient of O₂.

[0048] Subsequently, the first nitride film 43 and the first TEOS film42 can be selectively removed by photolithography and etching processesto form a contact hole 44 exposing a portion of the semiconductorsubstrate 41.

[0049] A second nitride film can be deposited on a surface of thesemiconductor substrate 41 and then etched back such that nitride filmspacers 45 can be formed at a side within the contact hole 44.

[0050] As shown in FIG. 5B, a polysilicon film can be deposited on thesemiconductor substrate 41 and in the contact hole 44. The polysiliconfilm can be then etched back to form a plug 46 within the contact hole44.

[0051] As shown in FIG. 5C, a second TEOS film 47 can be deposited onthe semiconductor substrate 41 and than selectively removed by thephotolithography and etching processes to form a trench 48 that exposesthe plug 46 and a surface of the first nitride film 43 adjacent to theplug 46.

[0052] Subsequently, as shown in FIG. 5D, a tungsten film 49 can beformed on the surface of the semiconductor substrate 41 by thesputtering method and the CVD method.

[0053] An SOG film 50 can be deposited on the entire surface of thesemiconductor substrate 41 and then selectively removed by the etch-backprocess, such that the film remains within the trench 48. The tungstenfilm 49 outside the trench 48 can be exposed.

[0054] As shown in FIG. 5E, the exposed tungsten film 49 can be removedby the CMP process. The tungsten film 49 remaining within the trench 48constitutes a lower electrode 49 a.

[0055] Subsequently, the remaining SOG film 50 can be removed by the wetetching process.

[0056] As shown in FIG. 5F, the second TEOS film 47 can be removed, anda Ta₂O₅ film 51 can be deposited on the surface of the semiconductorsubstrate 41. The Ta₂O₅ film 51 can be then oxidized by flowing oxygenunder the ambient of hydrogen gas at a temperature of between about 800°C. and about 850° C. During the oxidation process, an amount of thehydrogen can be greater than or equal to the amount of the oxygen.

[0057] The Ta₂O₅ film 51 can be re-oxidized by an UV-O₃ process. TheTa₂O₅ film 51 can be irradiated by light having a wavelength of betweenabout 250 to about 260 nm that can be generated by a UV-lamp, in anatmosphere of O₃ produced by an O₃ generator.

[0058] A metal film for an upper electrode can be deposited on theentire surface of the Ta₂O₅ film 51. A titanium nitride (TiN) film or atungsten(W) film can be used as the metal film for an upper electrode.

[0059] The metal film for the upper electrode can be selectively removedby the photolithography and etching processes, such that the metal filmremains on the Ta₂O₅ film 51 on both the lower electrode 49 a and aregion adjacent to the lower electrode 49 a. By this process, an upperelectrode 52 can be formed. Thus, a capacitor of a semiconductor deviceaccording to another embodiment of the invention can be fabricated.

[0060] As shown in FIG. 6, a leakage current at an operational voltageof the device is decreased as compared to a leakage current for asemiconductor fabricated from a known method.

[0061] The methods for fabricating a capacitor of a semiconductorsubstrate according to the invention have the following advantages.

[0062] Since the Ta₂O₅ film can be oxidized at a relatively hightemperature, the efficiency of the oxidation process can be improved.Thus, the electrical characteristics of the Ta₂O₅ film are improved.Further, because oxidation of the lower electrode can be prevented, theleakage current characteristics of the electrode are improved.

[0063] The foregoing embodiments and advantages are merely exemplary andare not to be construed as limiting the present invention. The presentteaching can be readily applied to other types of apparatuses. Thedescription of the present invention is intended to be illustrative, andnot to limit the scope of the claims. Many alternatives, modificationsand variations will be apparent to those skilled in the art. In theclaims, means-plus-function clauses are intended to cover the structuresdescribed herein as performing the recited function and not onlystructure equivalents but also equivalent structures.

What is claimed is:
 1. A method for fabricating a capacitor of asemiconductor device on a semiconductor substrate, comprising: formingan insulating film on the semiconductor substrate; forming a plug in theinsulating film, the plug electrically connected with the semiconductorsubstrate; forming a lower electrode on the plug and the insulating filmadjacent to the plug; forming a Ta₂O₅ film on the lower electrode andthe insulating film adjacent to the lower electrode; oxidizing the Ta₂O₅film by flowing oxygen under the ambient of hydrogen gas at atemperature of between about 800° C. and about 850° C.; and forming anupper electrode on the Ta₂O₅ film on the lower electrode and theinsulating film adjacent to the lower electrode.
 2. The method accordingto claim 1, wherein forming the insulating film includes forming a TEOSfilm and a nitride film.
 3. The method according to claim 1, furthercomprising: oxidizing the insulating film under the ambient of O₂. 4.The method according to claim 1, wherein forming the plug furtherincludes selectively removing the insulating by photolithography andetching processes to form a contact hole exposing a portion of thesemiconductor substrate, depositing a metal film on a surface of theinsulating film and the contact hole, and selectively removing a portionof the metal film such that the metal film in the contact hole.
 5. Themethod according to claim 1, wherein forming the lower electrode furtherincludes depositing a metal film on the insulating film and the plug,and selectively removing a portion of the metal film by photolithographyand etching processes such that the metal film remains the plug and theinsulating film adjacent to the plug.
 6. The method according to claim1, further comprising: re-oxidizing the oxidized Ta₂O₅ film by UV-O₃process.
 7. The method according to claim 1, wherein forming the upperelectrode further includes depositing a metal film on the Ta₂O₅ film,and selectively removing the metal film by photolithography and etchingprocesses such that the metal film remains on the Ta₂O₅ film.
 8. Themethod according to claim 1, further comprising: selectively removingthe insulating film to form insulating film spacers.
 9. The methodaccording to claim 4, wherein the metal film comprises a polysiliconfilm.
 10. The method according to claim 5, wherein the metal filmcomprises a tungsten film.
 11. The method according to claim 6, whereinreoxidizing further includes irradiating light to form O₃, and excitinglight to form O₃.
 12. The method according to claim 7, wherein the metalfilm comprises at least one of a titanium nitride (TiN) film and atungsten(W) film.
 13. The method according to claim 8, wherein theinsulating film comprises a nitride film.
 14. The method according toclaim 11, wherein the light has a wavelength of between about 250 nm toabout 260 nm.